LEETCODE: Count and Say

最新推荐文章于 2025-12-03 17:03:32 发布

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本文介绍了一种特殊的整数序列——计数与描述序列，并提供了一个C++实现方案来生成该序列的第n项。通过不断迭代和读取前一项的数字模式，算法能够高效地构建出目标序列。

The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 111221, ...

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.

Given an integer n, generate the nth sequence.

Note: The sequence of integers will be represented as a string.

如果你看出了规律就很好理解了。

class Solution {
public:
    string countAndSay(int n) {
      string pre = "1";
      for(int ii = 2; ii <= n; ii ++) {
         string current;
         for(int jj = 0; jj < pre.length(); jj ++) {
            int kk = jj;
            while(kk + 1 < pre.length() && pre[kk] == pre[kk + 1]) {
               kk ++;
            }
            current += '0' + (kk - jj + 1);
            current += pre[jj];
            jj = kk;
         }
         pre = current;
      }

      return pre;
    }
};